The following relates generally to wireless communication, and more specifically to notifying whether an Internet Protocol (IP) Multimedia Subsystem (IMS) service is available to a mobile device. Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems.
A wireless multiple-access communications system may include access points supporting communication for multiple devices. Access points may communicate with devices on downstream and upstream links. Each access point has a coverage range, which may be referred to as the coverage area of the access point. Some access points may be multimode access points simultaneously supporting communications over multiple radio access technologies. For example, a multimode access point may concurrently communicate with a mobile device (i.e., a wireless station) over a WLAN or Wi-Fi network and a cellular base station over a cellular network. The multimode access point may provide bridging services (e.g., wireless fidelity (Wi-Fi) hotspot services) between the mobile device and the base station where the mobile device accesses services of the base station through the multimode access point.
A mobile device (e.g., cellular phone, laptop computer, tablet computer, desktop computer, etc.) communicating with a multimode access point may desire to access a service of a base station in communication with the multimode access point over a cellular network. In some cases, the availability of the service for the mobile device depends on the configuration of the base station, channel conditions between the multimode access point and the base station, network loading, or other factors. Because the multimode access point maintains the connection with the base station, the mobile device may be unaware of what services are available from the base station and, therefore, initiate an activity (e.g., a voice call) based on an assumption that the service is available. When the service is not available, however, attempted access to the service may time out before ultimately failing, thereby introducing unnecessary delay.